Matrix display device

ABSTRACT

A matrix display device comprises a matrix of optically addressable pixels (Pij) which comprise a light sensitive element (LSij) and a pixel light generating element (LGij). The light generating element (LGij) will produce a pixel light (LMij) with a brightness which depends on the state of the light sensitive element (LSij). The state of the light sensitive element (LSij) depends on the amount of light impinging on it. The actual brightness of the pixel light generating element (LGij) may further depend on a voltage across it. The pixels (Pij) are constructed such that a portion of the pixel light (PLMij) generated by the pixel light generating element (LGij) reaches the associated light sensitive element (LSij) of the pixel (Pij). The light sensitive element (LSij) is sensitive to the portion of the pixel light (PLMij) to obtain a feedback of the portion of the pixel light (PLMij) to the light sensitive element (LSij). This feedback may be used to obtain a memory behavior of the pixel (Pij) or to influence an intrinsic memory behavior of the pixel (Pij).

The invention relates to an active matrix display, and a displayapparatus comprising a matrix display.

U.S. Pat. No. 6,215,462 discloses a matrix display device with aplurality of rows of pixels. The rows of the matrix display are selectedone by one. Each row is associated with a light waveguide whichtransports light generated by a first light emission element to thepixels of the row. A particular row is selected if the associated selectlight emission element produces light; all the other rows are notselected because their associated select light emission elements do notproduce light.

Each pixel comprises a series arrangement of a light sensitive elementand a pixel light emission element. A data voltage in accordance withthe image data to be displayed is supplied to the series arrangement viacolumn conductors. In the selected row of pixels, the light generated bythe select light emission element associated with the selected rowreaches the pixels of the selected row via the associated lightwaveguide. Consequently, the light sensitive elements of the pixels ofthe selected row have a low impedance, and the data voltage occurssubstantially over the pixel light emission elements of the pixels ofthe selected row. Thus, the selected row of pixels will generate anamount of light in accordance with the image data presented on thecolumn conductors which each are connected to a column of pixels. In therows which are not selected, the select light emission elements do notproduce light, and thus the impedance of the light sensitive elements ofnot selected pixels is high. For these pixels, the data voltage willsubstantially occur across the high impedance of the light sensitiveelements, and consequently, the voltage across the pixel light emissionelements will be below a threshold value such that the pixel lightemission elements will not produce light.

It is an object of the invention to provide a matrix display with anincreased brightness.

A first aspect of the invention provides a matrix display as claimed inclaim 1. A second aspect of the invention provides a display apparatusas claimed in claim 10. Advantageous embodiments are defined in thedependent claims.

The matrix display device in accordance with the first aspect of theinvention comprises a matrix of optically addressable pixels. The pixelscomprise a light sensitive element and a pixel light generating element.The light generating element will produce a pixel light with abrightness which depends on the state of the light sensitive element.The state of the light sensitive element depends on the brightness oflight impinging on it. The actual brightness of the pixel lightgenerating element may further depend on a pixel voltage across it.

The pixels are constructed such that in a pixel a portion of the pixellight generated by the pixel light generating element reaches theassociated light sensitive element of the pixel. The light sensitiveelement is sensitive to the pixel light to obtain an optical feedback ofthe portion of the pixel light to the light sensitive element.

This feedback may be used to obtain a memory behavior of the pixel or toinfluence the memory behavior of the pixel. With respect to the priorart U.S. Pat. No. 6,215,462, the memory behavior of the pixel will causethe pixel which is switched on during an addressing period to stay onafter the addressing period. The pixel will generate light duringsubstantially the whole frame period and not only during the addressingperiod, and consequently its brightness increases.

The optical feedback may also be used to influence an intrinsic memorybehavior of a pixel caused by a capacitance of the pixel. The portion ofthe light impinging on the light sensitive element is used to dischargethe capacitance, as is defined in the embodiment of the invention ofclaim 5.

In an embodiment in accordance with the invention as claimed in claim 2,the pixel voltage is supplied across a series arrangement of the pixellight generating element and an impedance element of which the impedancedepends on the state of the light sensitive element. If the pixelvoltage has a sufficiently high level and the impedance of the impedanceelement is low, the pixel light generating element will generate lightbecause the pixel voltage is substantially present across it. If thepixel voltage has a sufficiently high level and the impedance of theimpedance element is high, the pixel light generating element will notgenerate light because the pixel voltage is substantially present acrossthe light sensitive element.

The brightness of the portion of the light generated by the pixel lightgenerating element which impinges on the associated light sensitiveelement is sufficiently high to keep the impedance of the impedanceelement relatively low with respect to the impedance of the pixel lightgenerating element. Thus, if the pixel light emitting element is broughtin a state in which it emits light, a portion of this light will keep orbring the light sensitive element in a state in which the pixel lightemitting element stays in the light emitting state.

In an embodiment in accordance with the invention defined in claim 3,the light sensitive element itself is arranged in series with the pixellight generating element. If the impedance of the light sensitiveelement is low with respect to the impedance of the pixel lightgenerating element, the pixel voltage supplied across the seriesarrangement of the light sensitive element and the pixel lightgenerating element will substantially occur across the pixel lightgenerating element and thus determine its brightness. If the impedanceof the light sensitive element is high with respect to the impedance ofthe pixel light generating element, the pixel voltage will substantiallyoccur across the light sensitive element and the pixel light generatingelement will have a substantial zero brightness.

Once the impedance of the light sensitive element is low, the pixellight generating element produces light of which a portion is receivedby the light sensitive element. As this portion of the light issufficient to keep the impedance of the light sensitive element low, amemory behavior of the pixel is obtained. Thus, once the pixel lightgenerating element produces light, the state of the light sensitiveelement will be kept in the state keeping the pixel light generatingelement in the light emitting state. Thus, the pixel will continue togenerate light when another line of pixels is addressed andconsequently, the brightness of the display is improved.

Thus, if the pixel light emitting element is brought in a state in whichit emits light, a portion of this light will keep or bring the lightsensitive element in a state in which the pixel light emitting elementstays in the light emitting state.

In an embodiment in accordance with the invention defined in claim 4, aswitching element has a main current path arranged in series with thepixel light generating element and a control electrode coupled to thelight sensitive element. This has the advantage that the impedance ofthe light sensitive element is less important. If light of the pixellight generating element impinges on the light sensitive element itsimpedance changes, which causes the switching element to get a lowimpedance. Thus, again a memory behavior of the pixel is obtained.

In an embodiment in accordance with the invention defined in claim 5,the matrix display further comprises an control light generating devicewhich generates control light which is directed towards the lightsensitive elements of the pixels. The control light generating devicesupplies light to the light sensitive elements of the pixels whichshould produce light, and the control light generating element suppliesno light to the light sensitive elements of the pixels which should notproduce light.

It is possible to supply the same voltage across the series arrangementof the pixel light generating element and the series impedance for allthe pixels. The series impedance may be the light sensitive element orthe main current path of the switch which is controlled by the lightsensitive element. The pixels may be driven in a bi-stable manner: ifthe light sensitive element of a particular pixel receives light fromthe control light generating device, the corresponding pixel lightgenerating element will produce light, if the light sensitive element ofa particular pixel receives no light from the control light generatingdevice, the corresponding pixel light generating element will notproduce light. It is possible to vary the pixel voltage across theseries arrangement per pixel to vary the brightness produced by thepixel light generating element per pixel.

In an embodiment in accordance with the invention defined in claim 6,the light generated by a plurality of control light generating elementsis transported to lines of pixels via light waveguides. For each line ofpixels only one control light generating element is used. The controllight produced by the control light generating element can be used toperform the selecting of the line of pixels. The line of pixelsassociated with one of the control light generating elements may extendin the row or column direction of the matrix display.

The addressing of the complete matrix of pixels is elucidated in the nowfollowing. If for example, for the ease of elucidation, the lightwaveguides extend in the column direction, and the rows of the matrixdisplay are selected one by one with the pixel voltage. A row isselected by supplying a high level pixel voltage across the seriesarrangement of the pixel light generating element and the seriesimpedance of the pixels of the selected row. The other rows are notselected because a low level pixel voltage is supplied across the seriesarrangements of the pixels of not-selected rows. The rows and columnsmay be interchanged. The high level pixel voltage is selected such thatthe pixel light generating element of the pixel which receives controllight will emit light while a pixel light generating element of a pixelwhich does not receive control light will not emit light. The lowvoltage is selected such that pixels which were addressed earlier toproduce light still will produce light while pixels which were addressedearlier to not produce light will not start producing light. Thus, thepixels in the selected row can be switched on or off by the controllight, while the state of the pixels in not selected rows is unaltered.

In an embodiment in accordance with the invention defined in claim 7,the control light generating device comprises a laser for scanning alongthe light sensitive elements of the pixels. The laser obviates themultiple light generating elements and light-waveguides otherwiserequired.

In an embodiment in accordance with the invention defined in claim 8,the control light generating device directs the control light towardsthe further light sensitive element. A short light pulse from thecontrol light generating device suffices to charge the capacitor via thefurther switching element. The capacitor is discharged by the lightsensitive element which receives a portion of the pixel light from thepixel light generating element.

In this manner, the behavior a phosphor of a cathode ray tube isimitated: in response to the control light pulse, the pixel starts witha high brightness which gradually decreases. The value of the capacitordetermines the time during which the brightness decreases to zero. Thebrightness and/or duration of the control light pulse determine the peakbrightness of the pixel. Further, it is an advantage that the brightnessof the pixel is substantially independent on the quality of the pixellight generating element if this is a (Poly) LED (light emitting diode).If the (poly) LED does not function well, it will take longer todischarge the capacitor, and thus, the net amount of light produced issubstantially equal.

Thus, now the intrinsic memory behavior of the pixels is influenced bythe feedback of the portion of the light generated by the pixel lightgenerating element which impinges on the light sensitive element.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows an embodiment of a matrix display apparatus with opticallyaddressed display cells having an optical feedback to obtain a memoryeffect of the pixels,

FIG. 2 shows an embodiment of a display cell in accordance with theinvention,

FIG. 3 shows another embodiment of a display cell in accordance with theinvention,

FIG. 4 shows another embodiment of a display cell in accordance with theinvention, and

FIG. 5 shows a display apparatus in accordance with the inventionwherein the display cells are addressed with a laser.

The same references in different Figs. refer to the same signals or tothe same elements performing the same function.

FIG. 1 shows an embodiment of a matrix display apparatus with opticallyaddressed display cells having an optical feedback to obtain a memoryeffect of the pixels.

The matrix display comprises a matrix of pixels Pij (P11 to Pmn) whichare associated with intersections of light-waveguides LWj (LW1 to LWn)and sets of two row electrodes REi1, REi2. The index i indicates the rownumber, the index j indicates the column number of the matrix display.The row electrodes REi1 and REi2 extend in the x-direction, thelight-waveguides LWj extend in the y-direction. In a transposed matrixdisplay, the x and y direction are interchanged.

A select driver SD supplies row voltages Vi1 to the row electrodes REi1and row voltages Vi2 to the row electrodes REi2. The pixel voltage SVioccurs between the row electrode REi1 and the row electrode REi2 of thei^(th) row.

A data driver DD receives input data ID to be displayed and controllight generating elements ALj which produce an control light Lj with abrightness depending on the input data ID and which cooperate with thelight waveguides LWj to supply the control light Lj generated to thelight sensitive elements LSij, FLSij (see FIGS. 2 to 4) of the pixelsPij.

A control circuit CO receives synchronization information SY to supply acontrol signal CS1 to the select driver SD to select the rows LRi ofpixels Pij one by one, and a control signal CS2 to the data driver DD tosupply the data for the selected row LRi.

The pixels Pij may be formed in a substrate (not shown), the rowelectrodes REi1 and the row electrodes REi2 may be present at oppositesides of the substrate. One of the row electrodes REi1 or REi2 may bestructured as an electrode plate instead of separated electrodes whichextend in the row direction.

FIG. 2 shows an embodiment of a display cell in accordance with theinvention. In FIG. 2, the display cell or pixel Pij comprise a seriesarrangement of a pixel light generating element LGij and a lightsensitive element LSij of which an impedance depends on the brightnessof light received. The series arrangement of the pixel light generatingelement LGij and the light sensitive element LSij is arranged betweenthe first row electrode REi1 and the second row electrode REi2 toreceive the pixel voltage SVi. The voltage on the first row electrodeREi1 is denoted by Vi1, the voltage on the second row electrode REi2 isdenoted by Vi2, the pixel voltage SVi is the difference of the voltagesVi1 and Vi2. A portion of the pixel light PLMij produced by the pixellight generating element LGij will reach the light sensitive elementLSij.

The operation of the pixel Pij is elucidated in the now following. Thebrightness of light falling onto the light sensitive element LSij is thecombination of the portion of the pixel light PLMij generated by thepixel light generating element LGij and the control light Lj during theaddressing period during which the pixel Pij is addressed.

Initially, the pixel Pij is in the off state, even if a considerablepixel voltage SVi is present across the series arrangement. The highimpedance of the light sensitive element LSij causes the pixel voltageSVi to be substantially present over the light sensitive element LSij,and thus a substantially zero voltage is present across the pixel lightgenerating element LGij.

If a particular pixel Pij should produce light during the addressingperiod when a row of pixels Pij is addressed, the control lightgenerating element ALj will emit control light Lj which reaches thelight sensitive element LSij. The impedance of the light sensitiveelement LSij will become low with respect to the impedance of the pixellight generating element LGij and the pixel voltage SVi will besubstantially present across the pixel light generating element LGij.The pixel light generating element LGij will start to emit the pixellight LMij. Upon switching off the control light Lj, the pixel Pijremains in the on-state since the portion of the light PLMij generatedby the pixel light generating element LGij is captured by the lightsensitive element LSij which keeps it impedance low. The pixel Pij isswitched off by reducing the pixel voltage SVi below a threshold value.The pixel Pij thus has an in-built memory brought about by opticalfeedback to the light sensitive element LSij.

If a particular pixel Pij should not produce light during the addressingperiod when a row of pixels is addressed, the control light generatingelement ALj will not emit control light Lj and the impedance of thelight sensitive element LSij will stay high.

To drive a complete matrix display with a video signal, all the pixelsPij have to be addressed during a field period to provide a field ofinput video data ID during this field period to the pixels Pij. The nextfield of input data ID is supplied to the pixels Pij during the nextfield period. During a field period, the rows of the matrix display areselected one by one.

Before writing data to the pixels Pij first all pixels Pij have to bereset to produce no light. This is possible by reducing the pixelvoltage SVi below a threshold value for all the rows. Then, a particularrow is selected during a line select period (also referred to as lineaddress period, or the addressing period of the pixels) by supplying apixel voltage SVi to this row which is sufficiently high. At the sametime the control light generating elements ALj are activated to producecontrol light Lj for the columns that correspond to the pixel positionswithin the addressed row that are required to be switched to theon-state wherein the pixel light generating element LGij should emitlight. Next, at the end of the line select period, the pixel voltage SViis lowered to a value that is sufficient to sustain the pixels Pijwithin this row, but that is too low to readdress the pixels Pij. Thusthe pixel voltage SVi in not selected rows is too low to alter the stateof the pixels Pij but not so low that the pixels Pij are reset.

If more grey scales are required it is possible to use the well knownsub-field drive method. Each subfield of the field period can beaddressed in the same manner as elucidated above for a field period.

The pixel light generating elements LGij and the control lightgenerating elements ALj may, for example, comprise small lasers, LED's(light emitting diodes), OLED's (Organic LED's), PolyLED's, smallincandescent lamps or fluorescent lamps, or light generating elements asused in plasma displays. The light sensitive elements may, for example,comprise LDR's (light dependent resistors), or LAS (light activatedthyristors or other light activated electronic switches).

Such an optical addressed display is inexpensive and relatively easy tomanufacture compared to an LCD. The dimensions are easily scalable, onlysimple two terminal memory elements are required, and a high lumenefficacy is possible.

FIG. 3 shows another embodiment of a display cell in accordance with theinvention. The pixel light generating element LGij is arranged in serieswith the main current path of a transistor TR1 ij between the first rowelectrode REi1 and the second row electrode REi2. The voltage on thefirst row electrode REi1 is denoted by Vi1, the voltage on the secondrow electrode REi2 is denoted by Vi2, the pixel voltage SVi is thedifference of the voltages Vi1 and Vi2. The light sensitive element LSijis arranged between the control electrode of the transistor TR1 ij andthe first row electrode REi1. An optional capacitor C1 ij is arrangedbetween the control electrode of the transistor TR1 ij and the secondrow electrode REi2. An optional leakage resistor RLij is also arrangedbetween the control electrode of the transistor TR1 ij and the secondrow electrode REi2.

If control light Lj impinges on the light sensitive element LSij, thetransistor TR1 ij becomes low-ohmic and the pixel voltage VSi issubstantially present across the pixel light generating element LGijwhich starts emitting pixel light LMij. A portion of the pixel lightPLMij impinges on the light sensitive element LSij which thus will keepthe pixel in the on-state even when the control light Lj is not anymoresupplied. The pixel light generating element LGij will stop emittinglight when the pixel voltage SVi drops below a particular value. Thepixel light generating element LGij can also be switched off (or on)with the voltage Vi3.

The capacitor C1 ij buffers the voltage on the control electrode of thetransistor TR1 ij and provides a memory behavior. The resistor RLijdischarges the capacitor and thus determines the time constant of thememory.

FIG. 4 shows another embodiment of a display cell in accordance with theinvention. The pixel light generating element LGij is arranged in serieswith the main current path of a transistor TR1 ij between the rowelectrode REi1 and the row electrode REi2. The voltage on the rowelectrode REi1 is denoted by Vi1, the voltage on the row electrode REi2is denoted by Vi2, the pixel voltage SVi is the difference of thevoltages Vi1 and Vi2. The light sensitive element LSij is arrangedbetween the control electrode of the transistor TR1 ij and the rowelectrode REi1. An optional capacitor C2 ij is arranged between thecontrol electrode of the transistor TR1 ij and the row electrode REi1. Amain current path of a transistor TR2 ij is arranged between the controlelectrode of the transistor TR1 ij and the second row electrode REi2. Alight sensitive element FLSij is arranged between the control electrodeof the transistor TR2 ij and the row electrode REi1.

If a short control light pulse Lj impinges on the light sensitiveelement FLSij, the transistor TR2 ij becomes low-ohmic and the capacitorC2 ij is charged to the pixel voltage VSi. The transistor TR1 ij startsconducting and the pixel light generating element LGij starts emittingpixel light LMij. The charge on the capacitor C2 ij will keep thetransistor TR1 ij conductive. A portion of the pixel light PLMijimpinges on the light sensitive element LSij which will discharge thecapacitor C2 ij. The impedance of the transistor TR1 ij will graduallyincrease. In this manner, the behavior a phosphor of a cathode ray tubeis imitated: in response to the control light pulse Lj, the pixel Pijstarts with a high brightness which gradually decreases. The value ofthe capacitor C2 ij determines the time during which the brightnessdecreases to zero. The brightness and/or duration of the control lightpulse Lj determine the peak brightness of the pixel Pij. Further, it isan advantage that the brightness of the pixel Pij is substantiallyindependent on the quality of the pixel light generating element if thisis a (Poly) LED (light emitting diode). If the (poly) LED does notfunction well, it well take longer to discharge the capacitor C2 ij, andthus, the net amount of light produced is substantially equal.

It possible to switch the pixel Pij off with the voltage Vi3 at thecontrol electrode of the transistor TR2 ij.

The optional parallel arrangement of the capacitor C3 ij and theresistor R3 ij is arranged between the control electrode of thetransistor TR2 ij and the electrode REi2. This parallel arrangementintegrates the effect of the light pulse Lj.

FIG. 5 shows a display apparatus in accordance with the inventionwherein the display cells are addressed with a laser. The opticaladdressable display device OAD comprises the pixels Pij and the rowelectrodes REi1 and REi2 as shown in FIG. 1. Usually the pixels Pij areintegrated in a substrate SU while the row electrodes REi1 and REi2 arepresent at opposite sides of the substrate SU. The light waveguides LWjare not present.

In the embodiment in accordance with the invention as shown in FIG. 1,the optical state of the pixels Pij is controlled by the control lightLj generated by the control light generating elements ALj which controllight Lj is transported via the light-waveguides LWj to the lightsensitive elements LSij of FIG. 2 or the light sensitive elements FLSijof FIG. 4.

In the embodiment in accordance with the invention as shown in FIG. 5, alaser LAS generates the control light Lj which has to impinge on thelight sensitive elements LSij of FIG. 2 or the light sensitive elementsFLSij of FIG. 4. The scanning of the laser beam LB produced by the laserLAS may be controlled with an x/y scanner SCA. This x/y scanner SCA ismechanically moveable to scan the laser beam LB along the lightsensitive elements LSij or FLSij of the display OAD. Preferably, thelaser beam LB scans over the rows LRi of the pixels Pij one by one. Itis also possible to use more than one laser beam LB.

The laser scanning simplifies the construction of the display becausethe light-waveguides LWj and the multiple control light generatingelements ALj are not required. Further, the data driver DD becomes lesscomplex as a single drive signal for a single laser LAS has to begenerated instead of the large amount of drive signals, one for eachcontrol light generating element ALj. In a preferred embodiment, thelaser LAS is only used to address the pixels Pij and not to generategray scales. Consequently, a simple diode laser suffices.

The display OAD has a simple construction and thus can be produced easyand cheap. The display OAD may even be a foil. The laser LAS may scanthe rear or the front of the display OAD. Rear projection has theadvantage that it is easy to prevent the ambient light to reach thelight sensitive elements LSij or FLSij. In a front projector, a filterlayer in the display OAD has to cover the light sensitive elements LSijor FLSij such that the ambient light is sufficiently blocked and doesnot influence the state of the pixels Pij, while the laser beam is ableto sufficiently pass the filter to be able to control the state of thepixels Pij. It is also possible to use light sensitive elements LSijwhich are sensitive to the laser light but not to the ambient light.

In a color display, the position of the laser beam LB on the displayscreen needs to be known to synchronize the intensity of the laser beamLB corresponding to the video information with the position of the Red,Green and Blue pixels of the display OAD.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims.

For example, the transistors which are shown to be MOSFETS, may also bebipolar transistors. All the transistors may be of the oppositeconductivity type, the circuits have to be adapted in a manner known tothe skilled person. The transistors may be based on inorganic materials(such as silicon) or organic materials.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word “comprising” does notexclude the presence of elements or steps other than those listed in aclaim. The invention can be implemented by means of hardware comprisingseveral distinct elements, and by means of a suitably programmedcomputer. In the device claim enumerating several means, several ofthese means can be embodied by one and the same item of hardware. Themere fact that certain measures are recited in mutually differentdependent claims does not indicate that a combination of these measurescannot be used to advantage.

1. A matrix display device with a matrix of optically addressable pixels(Pij) comprising a pixel light generating element (LGij) for generatingpixel light (LMij), and a light sensitive element (LSij) being sensitiveto the pixel light (LMij), wherein the light sensitive element (LSij)and the pixel light generating element (LGij) are positioned withrespect to each other to enable pixel light (LMij) generated by thepixel light generating element (LGij) to reach the light sensitiveelement (LSij) to obtain an optical feedback of a portion of the pixellight (PLMij) from the pixel light generating element (LGij) to thelight sensitive element (LSij).
 2. A matrix display as claimed in claim1, wherein the pixel light generating element (LGij) and an impedanceelement (LSij; TR1 ij) are arranged in series, an impedance of theimpedance element (LSij; TR1 ij) being dependent on a state of the lightsensitive element (LSij), and wherein the matrix display furthercomprises a pixel driver (SD, DD) for supplying a pixel voltage (SVi) tothe series arrangement of the impedance element (LSij; TR1 ij) and thepixel light generating element (LGij).
 3. A matrix display device asclaimed in claim 1, wherein the impedance element (LSij; TR1 ij)comprises the light sensitive element (LSij), and wherein the portion ofthe pixel light (PLMij) reaching the light sensitive element (LSij) issufficient for keeping an impedance of the light sensitive element(LSij) relatively low with respect to an impedance of the pixel lightgenerating element (LGij).
 4. A matrix display device as claimed inclaim 2, wherein the impedance element comprise a switching element (TR1ij) having a main current path arranged in series with the pixel lightgenerating element (LGij), and having a control electrode coupled to thelight sensitive element (LSij), and wherein the portion of the pixellight (PLMij) reaching the light sensitive element (LSij) is sufficientfor obtaining an impedance of the switching element (TR1 ij) beingrelatively low with respect to an impedance of the pixel lightgenerating element (LGij).
 5. A matrix display device as claimed inclaim 1, wherein the display device comprises an control lightgenerating device (ALj; LAS) for generating control light (Lj) beingdirected towards the light sensitive element (LSij) of the opticallyaddressable pixels (Pij) to address the pixels (Pij).
 6. A matrixdisplay device as claimed in claim 5, wherein the control lightgenerating device (ALj) comprises a plurality of light generatingelements (ALj) and light waveguides (LWj) for transporting the light(Lj) generated by the plurality of light generating elements (ALj) tolines (LVj) of the pixels (Pij).
 7. A matrix display device as claimedin claim 5, wherein the control light generating device (ALj; LAS)comprises a laser (LAS) for generating a laser beam, and deflectionmeans (SCA) for scanning the laser beam along the light sensitiveelements (LSij) of the pixels (Pij).
 8. A matrix display device asclaimed in claim 5, wherein the display device comprises an controllight generating element (ALj) for generating control light (Lj) beingdirected towards the optically addressable pixels (Pij) to address thepixels (Pij), and wherein the pixels (Pij) further comprise: a furtherlight sensitive element (FLSij) for receiving the control light (Lj), acapacitor (C2 ij) coupled to the control electrode of the switchingelement (TR1 ij), and a further switching element (TR2 ij) having acontrol electrode coupled to the further light sensitive element (FLSij)and a main current path coupled to the control electrode of the firstmentioned switching element (TR1 ij).
 9. A matrix display device asclaimed in claim 1, wherein the light sensitive element (LSij) is alight-dependent resistor or a light-activated switch.
 10. A displayapparatus comprising a matrix display as claimed in claim 1 wherein thepixels (Pij) are arranged in successive lines (LRi) extending in a firstdirection (x), and the further light generating elements (Lj) areassociated with lines (LVj) of pixels (Pij) extending in a seconddirection (y) substantially perpendicular to the first direction (x),and wherein the display apparatus further comprises: a select driver(SD) for supplying pixel voltages (SVi) to the pixels (Pij) of the lines(LRi) of pixels (Pij) extending in the first direction (x) to select thepixels (Pij) of the lines (LRi) of pixels (Pij) extending in the firstdirection (x) line by line, a data driver (DD) for activating thefurther light generating elements (ALj) to supply light in accordancewith display data (ID) to be displayed to the light sensitive elements(LSij) of the lines (LVj) of the pixels (Pij) extending in the seconddirection (y).
 11. A display apparatus as claimed in claim 9, whereinone of the pixel voltages (SVi) associated with a selected one of thelines (LRi) are selected sufficiently high to enable the pixel lightgenerating element (LGij) to produce light (LMij; FLMij) when the light(Lj) of the further light generating element (ALj) reaches theassociated light sensitive element (LSij), and to produce no light whenno light is received from the further light generating element (ALj),while pixel voltages (SVi) associated with not selected lines (LRi) isboth not high enough and not too low to alter a state of the associatedpixel light generating element (LGij).